CHAPTER IX 

 GASTRIC SECRETION AND DIGESTION 



IT was in the eighteenth century that the chemical 

 factors in digestion were first clearly separated from the 

 mechanical. The accounts which have been preserved 

 of the experiments of Reaumur (1752) and of Spallanzani 

 (1777) are of extraordinary interest. An entertaining 

 summary is to be found in Foster's "Lectures on the His- 

 tory of Physiology," Chapter VIII. These ingenious 

 investigators were the first to show that digestive changes 

 may be caused to take place outside the body and in the 

 absence of any mechanical process whatever. They 

 obtained small quantities of gastric juice from various 

 animals, mixed it with food in flasks and test-tubes, and 

 watched for signs of alteration. Spallanzani, in particular, 

 succeeded in bringing about considerable solution of his 

 samples. . 



From that time to the present studies of digestion have 

 continued. Where the pioneers were forced to be content 

 with observing the dissolving of solid food, their successors 

 are drawing inferences regarding the transformations of 

 unseen molecules. A deeper insight into the meanings 

 of digestion became possible as the new science of organic 

 chemistry was swiftly advanced by the researches of 

 Wohler, Berzelius, and Liebig. As was pointed out in 

 Chapter III, it is the molecular change which is significant 

 and not the physical. Experiments in which material is 

 introduced intp the alimentary canals of animals and later 

 withdrawn for analysis are constantly compared with 

 trials in which the digestion takes place throughout in the 

 thermostats of the laboratory. 



The stomach is popularly supposed to have a very large 

 share in the total work of digestion. It cannot, however, 



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